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Show 1867.] DR. BOWERBANK ON ALCYONCELLUM SPECIOSUM. 355 are immersed in the sand, as appears to have been the case with the greater number of the specimens that I have examined, or when inserted in, or adherent to the tissues of another sponge, as in the case of the specimen in the possession of Dr. A. Farre. The recurvo-quaternate terminations of their distal ends are short and stout; and the terminal boss whence they spring is very strongly produced, so as to give them great retentive power. There are usually but four hooks; but in one instance I observed that number was doubled by each ray being replaced by two somewhat smaller ones. The shaft of the spiculum is barbed alternately at nearly regular distances for about one-fourth of its length from the recurvo-quaternate apex, the barbs pointing towards the smooth attenuating basal portion of the shaft, and they decrease in length and number from the apex of the spiculum downward. The structure of the apex of the fibre, combined with the numerous stout spines of the distal portion of the shaft, gives them remarkably strong prehensile power. These organs occur in large fasciculi, each consisting of numerous spicula. Their basal portions are clustered around the primary lines of the skeleton near their bases, and are firmly cemented to them for about a half or one-third of their length, from which attachment they ultimately pass off, diverging in various directions in search of points of adhesion. Their length frequently exceeds 3 inches. Athough siliceous, they are remarkably flexible and strong. The shaft consists of numerous concentric layers containing comparatively a large amount of animal matter. The structure of the fibre of this sponge is solid and siliceous, like that of Dactylocalyx ; but the mode of its disposition in the skeleton is very different. The primary lines consist of nearly parallel continuous fibres anastomosing laterally at irregular distances; so that in the aggregate they form a single circular series of strong and rigid compound columns of support bounding the large tubular internal cavity, and firmly braced in their proper positions by the secondary series of similarly constructed fibres, placed at right angles to the primary ones. This arrangement is further strengthened hy numerous small fibres disposed in various diagonal lines to the primary and secondary series of the skeleton-tissues. This admirable arrangement produces a structure combining the greatest amount of lightness, strength, and beauty that can well be conceived to exist in nature. At a short distance above the base of the sponge it is further strengthened by numerous strongly produced angular ridges of fibrous tissue disposed in lines which are always more or less diagonal to the long axis of the sponge, and usually somewhat flexuous. The ridges are but slightly produced near the base of the sponge, but they increase both in height and strength as they approach its apex. The summits of the ridges are composed of strong lines of anastomosing fibres; and two or three such lines of fibres are frequently to be seen beneath the outer one. These ridges do not appear to have ever formed portions of the terminal ridge or frill of the sponge, bounding the oscular area, although they agree perfectly in the mode of their structure; and it is probable that the circular |